Same framework for node backend and frontend
Same framework for Angular and React
No browser-specific bugs can be discovered with it
One of the reasons for not using Jest, might be because you want to use Karma tests. However, in some situations, the way that the tests are written, is that it would make it very difficult to run them in parallel. In addition, it might be difficult to convert tests from karma over to Jest. For 3000 tests, it might take a couple of days to move it over to jests.
Plan of action, we might have the option to only write jests tests, and then move over to karma, after writing for a month, and being used for the tests.